This invention relates to internal combustion engines, and in particular a method and control system for use in such engines to control the revolutionary speed thereof. The invention will in the main be described in relation to a direct injection two-stroke spark ignition engine, although it is to be appreciated that use of the method and control system in relation to other engine applications is also envisaged.
Internal combustion engines are used in a wide variety of applications, such as in motor vehicles (cars, all terrain vehicles and two-wheeled vehicles) and watercraft including personal watercraft (PWC""s) and outboard engines for boats. In many of these applications, it may be important in the operation of the engine to be able to control the rotational speed of the engine.
For example, a requirement to limit engine speed may arise in order to protect an engine from damage which could be sustained during overly high speed operation, or to limit the overall speed of the vehicle being powered by the engine. Such speed limiting may be desirable in instances where the operator of the vehicle is inexperienced or if maximum speed limits are provided for a given situation.
PWC""s are particularly susceptible to overspeed conditions as these craft are often operated at or near their maximum engine speed. During wave jumping for example, a popular activity of PWC enthusiasts, and during rough water conditions, the driving mechanism of the PWC is liable to rise above the water level, thereby creating a sudden drop in load on the engine, and hence an associated increase in engine speed. In this regard and since it is common for PWC""s to be operating at or close to maximum engine speed when wave jumping or in rough water, it is important to avoid any xe2x80x9cover-revvingxe2x80x9d of the PWC engine as this may result in damage to the engine.
In the past most engines simply had no maximum speed control except for the engine""s natural maximum limit, leaving the engine particularly susceptible to damage from operation at overly high speed. More recently, mechanical devices such as governors have been used, and developments in the electronic control of engines have resulted in a greater ability to control or restrict the maximum speed of internal combustion engines.
For example, in one such development, it has been proposed to prevent further increases in engine speed once the engine reaches a preset upper speed limit by skipping combustion events. In one possible scenario, the ignition event is simply not enabled, and the combustion event does not occur. This method however has the disadvantage that fuel is still delivered into the combustion chamber, and passes out through the engine exhaust system into the environment, in an unburnt state. This is both a significant waste of fuel and can be harmful to the environment. Additionally, residual unburnt fuel can remain in the combustion chamber and adversely affect a subsequent combustion event by reducing the predictability and certainty with regard to the amount of fuel in the combustion chamber.
Another known option is to reduce the fuelling level to the engine so that reduced power is produced thereby and engine speed is reduced. However, whilst this appears to be a reasonable option, bulk air flow through the combustion chamber is not affected by simply reducing the fuelling levels, and the overall result, particularly in the case of wide open throttle operation, may be enleanment of the air fuel ratio of the combustion mixture in the combustion chamber. Such enleanment can result in lean misfire and the overheating of the engine, particularly at high operating loads.
The present Applicant has developed a two-fluid fuel injection system as disclosed in, for example, the Applicant""s U.S. Pat. No. 4,693,224, the contents of which are incorporated herein by reference. The method of operation of such a two-fluid fuel injection system typically involves the delivery of a metered quantity of fuel to each combustion chamber of an engine by way of a compressed gas, generally air, which entrains the fuel and delivers it from a delivery injector nozzle. Typically, a separate fuel metering injector, as shown for example in the Applicants U.S. Pat. No. 4,934,329, delivers, or begins to deliver, a metered quantity of fuel into a holding chamber within, or associated with, the delivery injector prior to the opening of the delivery injector to enable direct communication with a combustion chamber. When the delivery injector opens, the pressurised gas, or in a typical embodiment, air, flows through the holding chamber to entrain and deliver the fuel previously metered thereinto to the engine combustion chamber.
In an engine operated in accordance with such a two-fluid fuel injection strategy, there are therefore distinct events in the combustion process, including a fuel metering or fuel event, an air delivery or injection event (as opposed to the bulk air delivery into the combustion chamber which occurs separately), and an ignition event. The engine management system typically required to implement such a strategy includes an electronic control unit which is able to independently control each of the fuel, air, and ignition events to effectively control the operation of the engine on the basis of operator input. Accordingly, the use of such a two-fluid fuel injection system allows combustion events to be partially or completely cancelled, producing a non-combustion event in a selected cylinder.
In the context of this specification, unless otherwise indicated, an xe2x80x9ceventxe2x80x9d is either a combustion event, or a non-combustion event which occurs where the combustion event would have occurred if it had been scheduled.
Hence, in a two-fluid fuel injection system, it is possible for the electronic control unit to simply cut one or more cylinders of the engine by simply providing no fuel for an event, the event then simply consisting of compressing air which is substantially free of fuel, and allowing it to expand again, thus not contributing to any additional engine speed and avoiding the negative consequences of other forms of engine speed control. However, simply cutting a fuel event may result in a certain degree of xe2x80x9cdryingxe2x80x9d of the delivery injector nozzle which would still have a quantity of air being delivered therethrough. This may result in the next combustion event upon reinstatement of the cut cylinder being less than satisfactory.
In a similar manner, it is possible for the electronic control unit to bypass or cut one or more cylinders of the engine by simply not initiating an air event. Thus, any fuel which is metered into the delivery injector nozzle is simply not delivered thereby, hence not contributing to any additional engine speed. However, such a strategy may also have associated problems in that upon reinstatement of the previously bypassed cylinder, the next combustion event may result in twice as much fuel being delivered to a cylinder. That is, the previous undelivered fuel quantity together with a subsequent metered quantity of fuel are delivered in the one injection event upon reinstatement of the previously bypassed cylinder.
It should be understood that cutting the ignition event as alluded to hereinbefore is still an option for producing a non-combustion event in such a two-fluid injection system, but this option still possesses the associated disadvantages as described hereinbefore.
Accordingly, in such a two-fluid injection system, it may be more beneficial to ensure that neither the fuel event nor the air event occur when seeking to cut a cylinder and hence produce a non-combustion event. In this regard, in order to effectively produce a non-combustion event in such a manner, it is obviously better to determine whether a particular combustion event should be skipped, and then arrange the cancellation of the fuel and air events prior to the start of the actual fuel metering for the combustion event.
However, in the above-mentioned two-fluid fuel injection system, the start of the fuel event, at high loads, may take place up to around 700 degrees before top dead centre (BTDC) of the compression stroke of the combustion event which is being scheduled, though it would more commonly occur at around 500-550 degrees BTDC for typical high load operation. A further complicating issue is that, together with the decision as to whether or not to provide a combustion event being made early, there may be a number of events which will affect the engine speed which are already scheduled to occur between the decision and the actual event occurring or not occurring. Further, the outcome of the impact of the event on the engine speed may not be known until some time after top dead centre (ATDC), possibly at around 180 degrees ATDC. Hence, the decision to have a combustion event or a non-combustion event is effectively needing to be made some time before the outcome of an earlier scheduled event is known (i.e., upon the engine speed).
Such a delay may correspond to about five combustion or non-combustion events in a typical two cylinder two-stroke engine and as a result of this, control of the engine speed can be unpredictable. That is, due to the way in which fuel and air events are scheduled by the electronic control unit, and also due to the processing delay within the electronic control unit, a decision to allow or cancel a combustion event will need to be made effectively two to three events prior to when the scheduled event would normally occur. This process is made somewhat more difficult by the fact that when this decision is made, depending on the engine operating speed, a number of other combustion events or non-combustion events may have already been scheduled and the effect that these events will have on the engine speed is unknown.
Whilst some of the above-mentioned difficulties are more pronounced in two-fluid fuel injection systems, similar difficulties may also be experienced with single fluid fuel injection systems.
Accordingly, it is an object of the present invention to provide an engine speed control method which at least ameliorates some of the above problems.
According to a first aspect of the present invention, there is provided a method of controlling the engine speed of an internal combustion engine, the method providing the steps of determining the speed of the engine at a given time, determining the change in the speed of the engine from a previous determination of the engine speed, and using the values for engine speed and change in engine speed to determine whether a future event should be a combustion event or a non-combustion event.
The determination of the change in the speed of the engine is effectively used to provide an indication of the overall load that the engine is experiencing. Hence, this determination can take account of a number of aspects which may effect the speed of the engine such as in particular the load placed on the engine due to its working environment. For example, in the case of a marine application, the change in engine speed and hence the overall load on the engine will be affected by whether the driving mechanism of the engine is in or out of the water.
Conveniently, the method as described is used to control the engine speed to a predetermined target speed. Hence, in determining whether a future event should be a combustion event or a non-combustion event, the method is providing for feed-forward control of the engine speed. That is, the method is applied to firstly effectively predict what the engine speed will be after one or a number of fuelling events in the future if the operating conditions remain unchanged, and then to decide whether the next events should be combustion events or non-combustion events so as to target a predetermined engine speed setting.
Preferably, where it is determined that a noncombustion event is required, no fuel is supplied to the combustion chamber. Alternatively, ignition may be cut such that a noncombustion event results in the respective combustion chamber. Other means of generating a non-combustion event may also be implemented.
Conveniently, fuel is supplied to the engine via a two-fluid direct fuel injection system, and where it is determined that a non-combustion event is required, no fuel is metered into a delivery injector of the two-fluid fuel injection system and no air is passed through the delivery injector into the combustion chamber. Hence, in such a two-fluid injection system, both the air and fuel events are cancelled where it is determined that a non-combustion event is required.
Preferably, a decision as to whether a particular event is to be a combustion event or a non-combustion event is made prior to the beginning of the fuelling operation for that event. The decision as to whether a particular event is to be a combustion event or a non-combustion event may be made at over 360 degrees BTDC for the event which is being determined, and may be at around 710 degrees BTDC. Essentially, at higher engine speeds, a decision will need to be made at such an earlier time as it is possible that one or more events are already scheduled to occur prior to the event for which the decision is being made. This is particularly the case for two-fluid fuel injection systems where it is typical at higher engine speeds for a number of fuel and air events to be already scheduled to occur prior to the event upon which the decision to cancel or enable the event is being made.
Preferably, the method is applied during high speed operation of the engine, and is used to avoid the occurrence of overspeed conditions. Conveniently, the method is applied to control the engine speed during high speed operation to a threshold target engine speed. Hence, the method is used to provide an indication of what the engine speed will be after one or a number of events in the future and to then control the engine speed to the threshold target speed by enabling a subsequent combustion event to occur or by deciding that a non-combustion event should occur. Thus, the method enables the operator or rider of the craft within which the engine is arranged to maintain the engine speed at or close to the maximum allowed speed without damaging the engine.
Accordingly, the method provides for feed-forward overspeed control by targeting a predetermined threshold engine speed and scheduling a sequence of combustion events and/or non-combustion events which will maintain the engine speed as close to the target engine speed as possible.
Preferably, the method is applied when the engine speed exceeds a predetermined entry speed. Conveniently, this entry speed is set at a value lower than the target or threshold speeds to which the engine speed is controlled. Hence, as the speed of the engine climbs towards the predetermined target or threshold speed, it will preferably only be controlled according to the present method once it exceeds the lower entry engine speed. This entry engine speed may typically be 1000 rpm less than the target engine speed.
Preferably, an adaption value is calculated on the basis of engine speed and the effective load levels as determined for a given event. The adaption value may be used in determining whether the future event should be a combustion event or a non-combustion event. Where the effective load on the engine is high, the adaption value may be set so as to increase the likelihood of a combustion event as compared to a non-combustion event. This is typically consistent with small changes in the engine speed such as for a marine engine operating at high speed with the driving mechanism of the engine continuously being located in the water. Where the effective load on the engine is low, the adaption value may be set so as to increase the likelihood of a non-combustion event as compared to a combustion event. This is typically consistent with larger changes in the engine speed such as when the driving mechanism of a marine engine operating at high speed leaves the water.
Preferably, a filter is applied to the rate of change of the adaption value to limit the rate of change of the adaption value. The filter may be dependent on whether the load on the engine is increasing or decreasing.
Conveniently, the fuelling level supplied to the engine may be used as a determination of the load on the engine. Conveniently, once it has been determined that the engine speed is likely to exceed the predetermined threshold engine speed, a preset pattern of combustion events and non-combustion events is implemented in at least one injector to control the engine speed in relation to the threshold engine speed.
According to a second aspect of the present invention, there is provided a control system for an internal combustion engine in which current engine speed and the change in engine speed from a previous determination are taken into account when determining whether a future event should be a combustion event or a non-combustion event.
Preferably, the second aspect of the present invention provides a control system for operation in accordance with each of the preferred embodiments of the first aspect of the present invention.
Specifically, there may be provided a system for targeting a predetermined threshold or target engine speed and scheduling a sequence of combustion events and/or non-combustion events which will maintain the engine speed as close to the target engine speed as possible.
The system may also be further adapted to provide for limitation of overspeed conditions in the use of the internal combustion engine.
Preferably, the system may provide an adaption value, which is calculated on the basis of engine speed and the effective load levels as determined for a given event. The adaption value may be used in determining whether a future event should be a combustion event or a non-combustion event.
According to a third aspect of the present invention, there is provided an Electronic Control Unit arranged to implement a control strategy for an internal combustion engine, in which current engine speed and the change in engine speed from a previous determination are taken into account when determining whether a future event should be a combustion event or an non-combustion event.
According to a fourth aspect of the present invention, there is provided a method of controlling the rotational speed of an internal combustion engine, the method including the steps of determining whether the engine speed is likely to exceed a predetermined threshold engine speed, and implementing a pattern of combustion events and non-combustion events in at least one engine cylinder in order to modify the effective fueling level to the engine cylinders so as to control the engine speed in relation to the threshold engine speed.
Preferably, the prevailing fueling level for an individual cylinder in which a combustion event is to occur is not altered. That is, whilst the effective fueling level to the engine may, for example, be reduced, the fueling level to the individual cylinders which are not cut (i.e., within which a combustion event will be allowed to occur) will remain unchanged. In this way, the operational cylinders will continue to operate with the same prevailing air/fuel ratio.
Preferably, the method of controlling the speed of the engine is affected so as to limit the engine speed. Preferably, the determination of whether the engine speed is likely to exceed the predetermined threshold engine speed is based on the engine speed determined for a given time. Preferably, the requirement for reduced speed may be determined on the basis of both the engine speed and the effective load on the engine whereby the latter is established by determining the change in engine speed from a previous determination thereof. In this regard, once it is determined that the engine speed will exceed a predetermined threshold engine speed and the effective load on the engine has been determined, the effective fueling level required to maintain the engine speed at the threshold engine speed can be calculated. On the basis of this desired effective fueling level, one of a number of preset patterns of combustion events and non-combustion events can be implemented to control the engine speed.
Preferably, the method of controlling the speed of the engine is effected by implementing a repeatable pattern of combustion events and/or non-combustion events.
Preferably, the method is used to avoid overspeed conditions in the engine operation. The pattern of combustion events and non-combustion events may provide a greater number of non-combustion events per sequence when there are effectively lower load conditions on the engine, and a lower number of non-combustion events per sequence when the engine effectively experiences higher load conditions.
Accordingly, the method of prescribing a sequence of combustion events and/or non-combustion events results in a reduction of the torque output of the engine and hence the speed thereof in a predictable manner. This is achieved without regulating or reducing the fuelling of a number of events and hence without running a variety of air/fuel ratios between different engine cylinders. This is particularly applicable to wide open throttle operation where the engine speed is typically close to the maximum operating speed of the engine wherein reduced fuelling levels may cause engine detonation and overheating.
Unless clearly indicated otherwise, the expression xe2x80x9ctop dead centrexe2x80x9d (TDC) shall be taken to refer to the location at top dead centre of a piston within a cylinder of a corresponding engine during the event which is being determined by the method or control system of the present invention. A reference to an angle xe2x80x9cbefore top dead centrexe2x80x9d (BTDC) or xe2x80x9cafter top dead centrexe2x80x9d (ATDC) shall be taken as a reference to the number of degrees of rotation of the engine before or after the top dead centre position for the event which is being determined by the method or control system of the present invention.
The method and control system of the current invention is particularly applicable to marine and PWC applications. It is also however conceived that this invention may also be applicable to other engine applications and hence the invention is not deemed to be limited in its application.
Further, whilst the current invention is particularly applicable to dual fluid fuel injection systems, it is not intended to be limited as such and can be equally applicable for use with single fluid fuel injection systems. Still further, the current invention has applicability to both two and four stroke cycle engines.